1. Field of the Invention
The present invention relates to hearing-aid fitting systems. More particularly, the present invention relates to a hearing-aid fitting system for a programmable hearing-aid device wherein the programmable hearing-aid device to be worn by the hearing-aid user is employed in the assessment of the hearing loss of the individual.
2. The Prior Art
In well-known methods of acoustically fitting a hearing compensation device A such as a hearing-aid to an individual, the threshold of the individual""s hearing is typically measured using a calibrated sound-stimulus-producing device and calibrated headphones. The measurement of the threshold of hearing takes place in an isolated sound room, usually a room where there is very little audible noise. The sound-stimulus-producing device and the calibrated headphones used in the testing are known in the art as an audiometer.
Generally, the audiometer generates pure tones at various frequencies between 125 Hz and 12,000 Hz that are representative of the frequency bands the tones are included in. These tones are transmitted through the headphones of the audiometer to the individual being tested. The intensity or volume of the pure tones is varied until the individual can just barely detect the presence of the tone. For each pure tone, the intensity of the tone at which the individual can just barely detect the presence of the tone, is known as the individual""s air conduction threshold of hearing. Although the threshold of hearing is only one element among several that characterizes an individual""s hearing loss, it is the predominant measure traditionally used to acoustically fit a hearing compensation device.
Once the threshold of hearing in each frequency band has been determined, this threshold is used to estimate the amount of amplification, compression, and/or other adjustment that will be employed to compensate for the individual""s loss of hearing. The implementation of the amplification, compression, and/or other adjustments and the hearing compensation achieved thereby depends upon the hearing compensation device being employed. There are various formulas known in the art which have been used to estimate the acoustic parameters based upon the observed threshold of hearing. These include industry hearing compensation device formulas known as NAL1, NAL2, and POGO. There are also various proprietary methods used by various hearing-aid manufacturers. Additionally, based upon the experience of the person performing the testing and the fitting of the hearing-aid to the individual, these various formulas may be adjusted.
In another method for fitting a hearing-aid using an audiometer, more than just the hearing threshold measurement in each audio band is employed to calibrate the hearing-aid to compensate for an individual""s hearing loss. In this method, known as loudness growth by octave band (LGOB), tones at various frequencies and of various intensities are presented at random to the individual being tested through the earphones of the audiometer. Each of the tones is then characterized by the person being tested according to the individual""s perception of loudness. For these measurements, a seven point scale is employed for each of the various frequency bands.
There are a number of substantial problems associated with each of these prior art methods for fitting a hearing-aid device. Some of these problems are due to the methodology employed to assess the hearing compensation required, some are due to the equipment used to perform the testing, and some are due to the manner in which the testing is performed.
For example, the hearing compensation assessment methodologies do not provide any manner of accurately comparing a series of tones covering the frequency spectrum to determine whether there is an equal perceived loudness for the tones across the frequency spectrum. In other words, these methodologies lack the facility to accurately assess whether a sound perceived as soft, medium or loud is equally perceived as soft, medium or loud across the frequency. Another problem arises from the known hearing compensation methodologies, because the formulas for estimating the hearing compensation from the tested hearing loss employ broad averages as a baseline that do not take into account the perceptual differences among the individuals being tested.
Further, when the audiometer apparatus includes earphones to supply the tones to an individual being tested, it is difficult to calibrate the output of the hearing-aid device to be worn by the individual to match the output of the headphones which were used to measure the hearing loss. Another problem associated with the use of headphones to present tones to the individual is that due to the unique acoustics of each individual""s ear canal, the acoustic response and therefore the perception by the individual of the sound provided by the headphones will be different from the perception of sound when the actual hearing-aid device is inserted into the ear canal.
Finally, once the hearing compensation provided by the hearing-aid has been set, and the hearing-aid has been inserted into the ear canal of the individual, the testing methods do not provide any satisfactory manner of performing an instantaneous comparison between a first fitting and a second fitting. This is known as A-B comparison. Typically, the amount of time required to perform an A-B comparison is either the amount of time needed to remove a device A and insert a second device B, or the 20 plus seconds required to update the programmed hearing compensation in a programmable hearing aid. This makes it difficult for an individual to accurately compare perceived differences in loudness in response to stimuli for the alternate fittings.
Accordingly, it should be appreciated that there is a need for a simple and accurate method of assessing the hearing loss of an individual to provide a successful fitting of a multi-band, broad dynamic range, programmable hearing compensation devices.
Further, it is an object of the present invention to measure the perception of loudness of an individual at multiple levels in each frequency band and to compare perceived loudness across a frequency bands for different dynamic levels.
Another object of the present invention to assess the hearing loss of individual by employing the hearing aid to be worn by the individual to generate the tones used to assess the hearing loss.
It is another object of the present invention to compensate for a variation in the electrical characteristics of the components employed in a hearing aid.
It is a further object of the present invention to simplify and make more accurate the comparison of alternate hearing compensation implementations in a programmable hearing aid.
A method for fitting a hearing compensation device according to the present invention comprises selecting a plurality of loudness levels for a plurality of frequencies and comparing each loudness level for each frequency for perceived sameness. The loudness levels may then be adjusted as needed to achieve perceived sameness across the frequency spectrum. A gain curve for each frequency is calculated from the selected plurality of loudness levels.